There are many situations in which it is important to be able to accurately detect particles above a predetermined size in a gas stream since a gas utilization device downstream of the detector will be damaged if encountered by a gas stream with particles. One particularly illustrative example of this is a gas turbine which utilizes hot combustion gases in order to do the mechanical work, generate electricity, or the like.
Gas turbines are particularly sensitive to particles in the hot combustion gas stream. Even a small number of particles over 10 micrometers in size will quickly damage a turbine blade, which not only requires replacement of the blade, but can shut down an entire facility for a significant period of time. For that reason, a wide variety of different particle separators have been devised, such as filters, centrifugal separators, and the like, which remove the particles before they get to the turbine. If the particle separator breaks down or is damaged, however, or a sudden change in the fuel causes differences in the particle load, potentially damaging particles can move past the particle separator, which will damage the turbine.
No known systems are in existence which will reliably determine the change in the quality of the stream of gases from a combustion facility to the turbine downstream of the particle separator. Conventional particle detecting or measuring devices typically are not capable of detecting small amounts of fine particles in large flows of gas, such as exist downstream of the particle separators in the flow of hot combustion gases to a turbine. Conventional detection systems may cause false alarms, or simply inadequately determine when potentially damaging particles (e.g. with a size greater than about 10 micrometers) flow in a post-particle separator gas stream.
According to the present invention, it is possible to adequately detect--and then take appropriate corrective action--when particles larger than a predetermined size are passing in a post-particle separator stream to a gas utilization device, such as a gas turbine. This is accomplished, according to the invention, by providing a particle concentrating means disposed between the particle separator and the gas utilization device, and providing a particle detecting means associated with the particle concentrating means. In response to the particle detecting means, an activity will be initiated which prevents damage to the gas utilization device, such as activating an alarm whereby an operator takes corrective action, putting an alternative/substitute particle separator on line, shutting down the combustor, etc.
According to the present invention, the particle concentrating means preferably comprises a generally linear first conduit extending to a branch section, and at the branch section the first conduit branches into second and third conduits. The second conduit is a substantial continuation of the first conduit, while the third conduit makes an angle with respect to the second conduit that is large enough that the vast majority of the particles in the first conduit having a size greater than the predetermined size will flow into the second conduit, while gas and primarily only particles having a size less than the predetermined size will flow into the third conduit. Typically the angle between the first and third conduits is about 90.degree..
The second conduit may either be a blind conduit, or may have a restricted flow of gas therethrough. Particularly where it is a blind conduit, a piezoelectric device may be mounted on the end termination of the second conduit. Alternatively, whether in a blind conduit or one with restricted flow, a signal transmitter and receiver may be disposed on opposite sides of the second conduit for detecting particles therein. Where the second conduit has restricted flow, a filter may be disposed therein and a differential pressure sensing means being provided for sensing the pressure differential of opposite sides of the filter. In this latter case, the restricted flow of gas which passes through the filter may be connected up to the gas turbine, or other device for utilization of clean gas.
According to another aspect of the present invention, a method of preventing damage to a device for utilizing gases that is easily damaged by particles of greater than a predetermined size (which size of particles is difficult to detect in non-concentrated form) is provided. The method comprises the steps of essentially sequentially: (a) Effecting removal of particles greater than the predetermined size from a gas stream. (b) Concentrating any particles greater than the predetermined size that remain in the gas stream. (c) Detecting the level of concentrated particles greater than the predetermined size. And, (d) in response to step (c) initiating activities that prevent damage to the gas utilization device. Step (d) is preferably practiced by activating an alarm. Where the gas utilization device is a gas turbine operated by hot combustion gases, steps (a)-(c) are practiced to remove, concentrate, and detect particles having a size of about 10 micrometers or greater. Steps (b) and (c) are preferably practiced utilizing the concentrating and detecting devices described above.
The invention also relates to an assembly for generating and using hot combustion gases. In particular the assembly may comprise: Means for combusting fuel to produce hot combustion gases having particles therein. Means for removing particles greater than a predetermined size from the hot combustion gases. A conduit extending from the particle removing means, and having a generally linear first section. A conduit second section comprising a restricted flow continuation of the first section; A conduit third section disposed at approximately a 90.degree. angle with respect to the first section and the second section. A turbine operatively connected to the conduit third section. And, particle detecting means operatively associated with the conduit second section.
It is the primary object of the present invention to provide effective protection for a gas utilization device that is susceptible to damage from particles greater than a predetermined size which flow in unconcentrated form in a large volume of gas. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.